1. Field of the Invention
The present invention relates to a high-turning and high-transonic blade for use in a blade cascade for an axial-flow compressor in which a large number of blades, e.g., ten or more, each having an intrados adapted to generate a positive pressure and an extrados adapted to generate a negative pressure, disposed in an annular fluid passage.
2. Description of Background Art
Japanese Patent Application Laid-open No. 7-83196 discloses a blade for an axial-flow compressor in which the distribution of curvature of an extrados of the blade is established so that the curvature is decreased from a leading edge down to a minimum value, increased therefrom up to a maximum value, and then decreased toward a trailing edge, whereby the generation of a shock wave at the leading edge is avoided to provide a reduction in pressure loss.
Japanese Patent Application Laid-open No. 9-256998 discloses a blade for a compressor in which the shape of an intrados and the shape of an extrados of a leading edge of the blade are asymmetric with respect to a mean camber line, whereby a sudden change in flow speed at the leading edge is prevented to provide an increase in compression efficiency.
U.S. Pat. No. 4,655,412 describes a wing for an airplane in which an extrados of the wing is divided into three regions of different curvatures to provide an enhancement in lift characteristic of the blade of the air plane so that the curvature is decreased steeply from a large value at a leading edge to a first minimum value in a first region extending to a position smaller than 10% of a chord length in the vicinity of the leading edge, and the curvature is varied from the first minimum value via a first maximum value to a second minimum value at a position smaller than 40% of the chord length in a following second region.
In the blade of the axial-flow compressor described in Japanese Patent Application Laid-open No. 7-83196, the distribution of curvature of the extrados at the leading edge is similar to that according to the present invention. However, this blade is of a type having an extremely small turning angle and is different in a basic shape and function from a blade of a high-turning type to which the present invention is applied.
In the blade of the axial-flow compressor described in Japanese Patent Application Laid-open No. 9-256998, the distribution of curvature of the extrados at the leading edge is similar to that according to the present invention. However, as a front portion or another portion of the distribution of curvature is subsonic, the operating condition and function of this blade is different from the blade to which the present invention is applied and in which the entire curvature distribution is supersonic.
In the wing described in U.S. Pat. No. 4,655,412, the distribution of curvature of the extrados at the leading edge is similar to that according to the present invention. However, as this blade is used in an airplane, even if this blade is used in a blade cascade for an axial-flow compressor to which the present invention is applied, a desired performance cannot be exhibited.